1. Field of the Invention
The present invention relates to a manufacturing method of a scale for a photosensor for detecting a position of a mobile body moving within a predetermined region.
2. Description of the Related Art
Printers have been known as peripheral equipments of computers. In such a printer, it is required to actuate a printing head in a predetermined position at the time of printing so as to form characters or graphic patterns with dots. In some types of printers, therefore, a position sensor is provided for sensing a position of a printing head while the printing head is moving.
As such a position sensor, conventionally, a transmission-type photosensor has been mainly used. For example, as shown in FIG. 11, such a transmission-type photosensor 12 is provided with a light-emitting element and a light-receiving element which are disposed in opposition to each other. The photosensor 12 is attached to a carriage 11 of a printing head 10, and a photosensor scale 13 fixed to a printer body is provided so as to pass through between the light-emitting element and the light-receiving element of the photosensor 12. In the scale 13, a number of slits are formed to constitute graduations of a scale at very small intervals in a belt-like metal plate. Light which has been emitted from the light-emitting element of the photosensor 12 and which has passed through a slit of the scale 13 is received by the light-receiving element, and the graduation indicated by the slit of the scale 13 is read. In such a manner, for example, in an ink printer, a printing head reaches a predetermined position corresponding to a graduation slit located at a predetermined number from a base line of the scale is detected so that ink is injected from the printer head.
However, the transmission-type sensor per se is constituted by a pair of light-emitting and light-receiving elements, and high accuracy is required for forming slits at very small intervals in a scale. Therefore, the transmission-type sensor is very expensive.
In addition, recently, demand for high-precision and high-density printing has become stronger. Accordingly, the intervals of the slits are required to be smaller and more accurate. It has become difficult for a conventional scale to satisfy such requirements.